linux-kernel - [PATCH V2] media: dvb-usb: Optimizing err() output

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Message-ID: <tencent_A5374A4B00744776B566CC3DD936EC960A09@qq.com>
Date: Tue, 14 Oct 2025 08:30:31 +0800
From: Edward Adam Davis <eadavis@...com>
To: eadavis@...com
Cc: linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org,
	mchehab@...nel.org,
	syzbot+480edd2cadb85ddb4bbe@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: [PATCH V2] media: dvb-usb: Optimizing err() output

syzbot reported a uninit-value in pctv452e_i2c_msg. [1]

When the snd_len or rcv_len check fails and jumps to failed, buf is
uninitialized, triggering the uninit-value issue.

Setting the err() output buf byte count to 0 before jumping to failed
before initializing buf and setting it to 7 after initializing buf avoids
this warning.

[1]
BUG: KMSAN: uninit-value in hex_string+0x681/0x740 lib/vsprintf.c:1220
 pctv452e_i2c_msg+0x82a/0x8f0 drivers/media/usb/dvb-usb/pctv452e.c:467
 pctv452e_i2c_xfer+0x2e6/0x4c0 drivers/media/usb/dvb-usb/pctv452e.c:502

Reported-by: syzbot+480edd2cadb85ddb4bbe@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=480edd2cadb85ddb4bbe
Signed-off-by: Edward Adam Davis <eadavis@...com>
---
V1 -> V2: subject typos

 drivers/media/usb/dvb-usb/pctv452e.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/dvb-usb/pctv452e.c b/drivers/media/usb/dvb-usb/pctv452e.c
index 5094de9a312e..3b6e86a8e9ff 100644
--- a/drivers/media/usb/dvb-usb/pctv452e.c
+++ b/drivers/media/usb/dvb-usb/pctv452e.c
@@ -420,7 +420,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
 	struct pctv452e_state *state = d->priv;
 	u8 *buf;
 	u8 id;
-	int ret;
+	int ret, plen = 0;
 
 	buf = kmalloc(64, GFP_KERNEL);
 	if (!buf)
@@ -432,6 +432,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
 	if (snd_len > 64 - 7 || rcv_len > 64 - 7)
 		goto failed;
 
+	plen = 7;
 	buf[0] = SYNC_BYTE_OUT;
 	buf[1] = id;
 	buf[2] = PCTV_CMD_I2C;
@@ -466,7 +467,7 @@ static int pctv452e_i2c_msg(struct dvb_usb_device *d, u8 addr,
 failed:
 	err("I2C error %d; %02X %02X  %02X %02X %02X -> %*ph",
 	     ret, SYNC_BYTE_OUT, id, addr << 1, snd_len, rcv_len,
-	     7, buf);
+	     plen, buf);
 
 	kfree(buf);
 	return ret;
-- 
2.43.0